Secreted Kunitz proteinase inhibitor (KPI) domain-containing forms of the amyloid beta-protein precursor (ABetaPP) are also known as the previously described cell secreted proteinase inhibitor designated protease nexin-2 (PN2). Extensive earlier work from our laboratory has shown that PN2/ABetaPP is a potent inhibitor of several key pro-thrombotic enzymes and can inhibit thrombosis in vitro. These defining biochemical features of PN2/ABetaPP, coupled with its abundance in brain and in circulating blood platelets, have suggested a role for this protein in regulating thrombosis during episodes of cerebral vascular injury. Hemorrhagic and ischemic strokes are major health issues that can lead to severe debilitation and morbidity. Both hemorrhagic and ischemic strokes involve alteration of pro-thrombotic pathways. A precise understanding of the molecules and mechanisms involved in regulating cerebral thrombosis during these deleterious vascular events remains unresolved. The goal of this study is to define the role of the proteinase inhibitory properties of the ABetaPP in regulating cerebral thrombosis during cerebral vascular injury. In this regard, the overall hypothesis that forms the basis for this proposal is that the proteinase inhibitory function of PN2/ABetaPP plays a significant role in regulating cerebral thrombosis during cerebral vascular injury. The three specific aims of this proposal are as follows. First, determine if specific over-expression of platelet PN2/ABetaPP in transgenic mice will decrease thrombus formation, brain lesion, and behavioral deficits associated with cerebral vascular injury. Second, determine if specific over- expression of PN2/ABetaPP in brain in transgenic mice will modulate cerebral thrombosis in models of intracerebral hemorrhage and transient focal ischemia. Third, determine if deletion of the proteinase inhibitory activity of PN2/ABetaPP, amyloid precursor-like protein 2 (APLP2), or both will increase thrombus formation, brain lesion, and behavioral deficits in models of cerebral vascular injury. Together, these proposed translational investigations, which stem from our extensive previous in vitro work on the proteinase inhibitory properties of PN2/ABetaPP, will provide new insight into important physiological functions of this protein that currently remain unknown. This may lead to new avenues for developing strategies to regulate cerebral thrombosis and limit damage to the brain as a consequence of hemorrhagic and ischemic stroke.